SpectraRust/src/synspec/math/idmtab.rs

//! Output of selected molecular line parameters (identification table).
//!
//! Translated from SYNSPEC54.FOR subroutine IDMTAB (line 16380).
//!
//! Computes and formats molecular line parameters for the identification
//! table output, including equivalent widths and line strengths.

use crate::synspec::math::inibla::{CL, BOLK};

// ============================================================================
// Constants
// ============================================================================

/// Conversion factor: ln(10) for log-gf
const C1: f64 = 2.302_585_1;

/// Conversion factor: gf offset
const C2: f64 = 4.201_467_2;

/// Conversion factor: energy to temperature
const C3: f64 = 1.438_788_6;

/// Strength category labels
const APB: &str = "    ";
const AP0: &str = "   .";
const AP1: &str = "   *";
const AP2: &str = "  **";
const AP3: &str = " ***";
const AP4: &str = "****";

// ============================================================================
// IDMTAB parameters
// ============================================================================

/// Parameters for a single molecular line.
pub struct IdmtabLine {
    /// Wavelength (Å)
    pub alam: f64,
    /// Molecule index
    pub imol: usize,
    /// Lower excitation potential (cm⁻¹)
    pub excl: f64,
    /// Log gf value
    pub gfm: f64,
    /// Van der Waals broadening
    pub grm: f64,
    /// Stark broadening
    pub gsm: f64,
    /// Van der Waals broadening (depth-dependent)
    pub gvdw: f64,
    /// Doppler width
    pub dop1: f64,
    /// Continuum opacity at line center
    pub absta: f64,
    /// Stimulated emission factor
    pub stim: f64,
    /// Molecular population ratio
    pub rrmol: f64,
    /// Temperature at standard depth (K)
    pub temp: f64,
    /// Electron density at standard depth
    pub elec: f64,
}

/// Result of IDMTAB computation for a single line.
pub struct IdmtabResult {
    /// Wavelength (Å)
    pub alam: f64,
    /// Molecule name
    pub molecule: String,
    /// Log gf
    pub gf: f64,
    /// Lower excitation energy (K)
    pub excl_k: f64,
    /// Line-to-continuum ratio (STR0)
    pub str0: f64,
    /// Equivalent width (mÅ)
    pub eqw: f64,
    /// Strength category label
    pub apr: &'static str,
    /// Depth index
    pub id: usize,
    /// Total broadening parameter
    pub agam: f64,
}

// ============================================================================
// IDMTAB implementation
// ============================================================================

/// Compute molecular line parameters for the identification table.
///
/// For a given molecular line, computes the line strength, equivalent width,
/// and strength category.
///
/// # Fortran original
///
/// ```fortran
/// SUBROUTINE IDMTAB
///   DO IL0=1,NLINML
///     ...compute STR0, EQW, APR...
///   END DO
/// END
/// ```
pub fn idmtab_compute(line: &IdmtabLine) -> IdmtabResult {
    let IdmtabLine {
        alam, imol: _, excl, gfm, grm, gsm, gvdw,
        dop1, absta, stim, rrmol, temp, elec,
    } = *line;

    // Total broadening parameter
    // Fortran: AGAM=(GRM+GSM*ANE+GVDW)*DOP1
    let agam = (grm + gsm * elec + gvdw) * dop1;

    // Absorption at line center
    // Fortran: ABCNT=EXP(GFM-EXCL/TEMP)*RRMOL*DOP1*STIM
    let abcnt = (gfm - excl / temp).exp() * rrmol * dop1 * stim;

    // Line-to-continuum ratio
    // Fortran: STR0=ABCNT/ABSTA
    let str0 = if absta > 0.0 { abcnt / absta } else { 0.0 };

    // Log gf
    let gf = (gfm + C2) / C1;

    // Lower excitation energy in K
    let excl_k = excl / C3;

    // Equivalent width estimate
    let ww1 = if str0 <= 1.2 {
        0.886 * str0 * (1.0 - str0 * (0.707 - str0 * 0.577))
    } else {
        str0.ln().sqrt()
    };

    let ww1 = if str0 > 55.0 {
        let ww2 = 0.5 * (std::f64::consts::PI * agam * str0).sqrt();
        if ww2 > ww1 { ww2 } else { ww1 }
    } else {
        ww1
    };

    // Equivalent width in mÅ
    // Fortran: EQW=ALAM/FREQ0*1.E3/DOP1*WW1
    // Since ALAM is wavelength and we don't have FREQ0 directly,
    // we use the relation: EQW ≈ ALAM * WW1 / (c/ALAM) / DOP1 * 1e3
    // Simplified: EQW = ALAM^2 / CL * 1e3 / DOP1 * WW1
    let eqw = alam * alam / CL * 1e3 / dop1 * ww1;

    // Strength category
    let str = eqw * 10.0;
    let apr = if str >= 1e4 {
        AP4
    } else if str >= 1e3 {
        AP3
    } else if str >= 1e2 {
        AP2
    } else if str >= 1e1 {
        AP1
    } else if str >= 1e0 {
        AP0
    } else {
        APB
    };

    IdmtabResult {
        alam,
        molecule: String::new(), // Filled by caller
        gf,
        excl_k,
        str0,
        eqw,
        apr,
        id: 0, // Filled by caller
        agam,
    }
}

#[cfg(test)]
mod tests {
    use super::*;

    fn create_test_line() -> IdmtabLine {
        IdmtabLine {
            alam: 5000.0,
            imol: 1,
            excl: 10000.0,
            gfm: -2.0,
            grm: 0.1,
            gsm: 0.01,
            gvdw: 0.05,
            dop1: 0.01,
            absta: 1e-10,
            stim: 1.0,
            rrmol: 1e-5,
            temp: 10000.0,
            elec: 1e14,
        }
    }

    #[test]
    fn test_idmtab_basic() {
        let line = create_test_line();
        let result = idmtab_compute(&line);

        assert!(result.alam > 0.0);
        assert!(result.str0.is_finite());
        assert!(result.eqw.is_finite());
        assert!(result.eqw >= 0.0);
        assert!(result.agam.is_finite());
    }

    #[test]
    fn test_idmtab_weak_line() {
        let mut line = create_test_line();
        line.rrmol = 1e-20; // Very weak line
        let result = idmtab_compute(&line);

        // Weak line should have small STR0
        assert!(result.str0 < 1.0);
        assert_eq!(result.apr, APB);
    }

    #[test]
    fn test_idmtab_strong_line() {
        let mut line = create_test_line();
        line.rrmol = 1e10; // Very strong line
        line.absta = 1e-20;
        let result = idmtab_compute(&line);

        // Strong line should have large STR0
        assert!(result.str0 > 1.0);
    }

    #[test]
    fn test_idmtab_strength_categories() {
        // Test that different strength values produce correct categories
        let mut line = create_test_line();

        // Weak line
        line.rrmol = 1e-15;
        let r = idmtab_compute(&line);
        if r.str0 <= 1.2 {
            // For weak lines, EQW is small
            assert!(r.eqw < 1.0 || r.apr == APB);
        }
    }
}